Hot spas are not only very popular, but also extremely healthy. Many people consider the right spa to have a temperature of 35-38°C, whereas relative humidity is kept low, around 15%. One of the things a hot spa offers is a salt bath.
Whoever has tried inhaling salt water when they have a cold knows its wholesome properties. Salt keeps your mucous membranes humid and softens the skin, which receives most of the benefits of a salt bath.
Other possibilities are Hamam hot spas, soft energetic Caldarium spas or the heat radiated from stone walls, floors or seats in a Tepidarium.